Outbreak of Vibrio parahaemolyticus Infection Associated with Eating Raw Oysters and
Clams Harvested from Long Island Sound -- Connecticut, New Jersey, and New York, 1998

During July-September 1998, an outbreak of Vibrio parahaemolyticus infections
associated with consumption of oysters and clams harvested from Long Island Sound occurred
among residents of Connecticut, New Jersey, and New York. This is the first reported
outbreak of V. parahaemolyticus linked to consumption of shellfish harvested from New York
waters. This report summarizes the investigation of this outbreak.

On August 10, 1998, a New York City resident with toxigenic V. cholerae O1 infection
who had not traveled recently was reported to the New York City Department of Health
(NYCDOH). NYCDOH initiated an investigation to determine the most likely source of the
infection. Using a broadcast facsimile, NYCDOH contacted all Queens County laboratories on
August 12 and, on August 26, asked selected infectious diseases physicians and all New
York City hospitals and laboratories to consider V. cholerae as a potential cause of
diarrhea and to report any confirmed or suspected Vibrio infections to the NYCDOH.
Although no additional V. cholerae infections were reported, 23 culture-confirmed cases of
V. parahaemolyticus were reported among residents of Connecticut, New Jersey, and New
York. Dates of illness onset ranged from July 21 through September 17 (Figure_1).

An investigation coordinated by the New York State Department of Health determined that
22 of 23 ill persons had eaten or handled oysters, clams, or crustaceans: 16 ate raw
oysters or clams, two ate steamed crabs, one ate crab cakes, one ate boiled crabs and
lobsters, one ate lobster roll, and one handled live crabs. The median onset of illness
following consumption of shellfish was 19 hours (range: 12-52 hours). Clinical histories
were available for 19 of the 23 ill persons; 17 (89%) had gastroenteritis and two (11%)
had bloodstream infections with lower extremity edema and bullae. Among patients with
gastroenteritis, reported clinical symptoms included diarrhea (100%), abdominal cramps
(94%), nausea (94%), vomiting (82%), fever (47%), bloody stools (29%), headache (24%), and
myalgia (24%). Median duration of gastrointestinal illness was 5 days.

Traceback investigations by local and state health departments identified the site of
harvest for oysters or clams eaten by 11 of the 16 patients. Oysters or clams eaten by
eight patients were harvested from Oyster Bay, off New York's Long Island Sound, during
August 4-27. Shellfish tags from oysters and clams eaten by the other three persons
indicated harvest areas elsewhere off Long Island or, in one case, Washington state (1) *.

During the outbreak period, mean surface water temperature measurements from 15 Oyster
Bay stations was 77.2 F (25.1 C), compared with cooler 1997 and 1996 measurements (74.1 F
{23.4 C} and 69.4 F {20.7 C}, respectively). On September 10, the New York State
Department of Environmental Conservation (NYSDEC) closed Oyster Bay to harvesting of
shellfish and recalled shellfish harvested from that area after August 10.

Laboratory testing of 12 V. parahaemolyticus clinical isolates, including the eight
traced to Oyster Bay, identified O3:K6 serotype. Pulsed-field gel electrophoresis (PFGE)
performed on four clinical isolates at the New York City Bureau of Labs indicated that
three isolates epidemiologically linked to Oyster Bay had indistinguishable PFGE patterns,
and the other isolate not linked to Oyster Bay had a distinctly different pattern. Oysters
harvested on five occasions from Oyster Bay during September 11-October 14 contained V.
parahaemolyticus at less than or equal to 120 colony forming units {cfu} per gram of
oyster meat. None of these environmental isolates matched the outbreak strain or other
clinical isolates by PFGE. On the basis of these results and a decline in water
temperature to 63.5 F (17.5 C), NYSDEC reopened Oyster Bay to commercial shellfish
harvesting on October 22. No additional culture-confirmed cases of V. parahaemolyticus
infection have been reported.

Editorial Note

Editorial Note: This is the fourth multistate outbreak of V. parahaemolyticus
infections in the United States since 1997, and the first associated with shellfish
harvested from the northeast Atlantic Ocean. Before 1997, foodborne outbreaks caused by V.
parahaemolyticus had been infrequently reported in the United States (1). During
1997-1998, multistate outbreaks of V. parahaemolyticus were associated with consumption of
raw or undercooked oysters harvested from the Pacific Northwest and Texas (2; CDC,
unpublished data, 1998).

V. parahaemolyticus is a halophilic, gram-negative bacterium that naturally inhabits
marine and estuarine waters. V. parahaemolyticus infections are usually acquired by
persons who eat raw or undercooked shellfish, particularly oysters, or whose skin wounds
are exposed to warm seawater. The most common clinical manifestation of infection is
self-limited gastroenteritis, but infections may result in septicemia that can be life
threatening (3,4). The concentration of V. parahaemolyticus in seawater increases with
increasing water temperature and corresponds with a seasonal increase in sporadically
occurring cases in warmer months (4). This outbreak and the recent outbreaks of V.
parahaemolyticus infections in the Pacific Northwest and Texas occurred during summer
months.

To reduce the risk for V. parahaemolyticus and other shellfish-associated infections,
persons should avoid eating raw or undercooked shellfish, particularly during warmer
months. Monitoring of environmental conditions, such as water temperature and salinity,
may help determine when shellfish harvesting areas should be closed and re-opened to
harvesting.

Guidelines regulating the harvesting of oysters and clams rely on quantitative
measurement of V. parahaemolyticus levels in oyster or clam meat. However, data from
recent outbreaks may require revision of these guidelines. The recommended action level of
V. parahaemolyticus per gram of oyster meat that must be detected in the absence of human
illness before closing oyster beds is greater than 10,000 cfu/g. Oyster samples that were
harvested from implicated beds in the Pacific Northwest in 1997 and Oyster Bay in 1998
yielded less than 200 V. parahaemolyticus cfu/g of oyster meat, indicating that human
illness can occur at levels much lower than the current action level.

Infection with V. parahaemolyticus is not a notifiable condition in most states,
including New York. This outbreak was detected only coincidentally because of enhanced
surveillance during an investigation of a case of V. cholerae O1. Health-care providers
treating patients with gastroenteritis who have a history of recent ingestion of raw or
undercooked shellfish should consider Vibrio infection and request a stool culture
specifically for Vibrio. Clinical laboratories should use thiosulfate-citrate-bile
salts-sucrose agar (TCBS), a selective medium for culturing for Vibrio spp., when
culturing stool specimens for Vibrio and should consider using TCBS for routine screening
of all stools specimens, at least during summer months.

CDC coordinates a passive Gulf Coast Vibrio surveillance system and the Foodborne
Diseases Active Surveillance Network (FoodNet) to monitor the incidence of Vibrio
infections. Because of these multistate outbreaks, all states should consider making
infections with V. parahaemolyticus and other vibrioses reportable, with referral of
clinical isolates to public health laboratories for confirmation and strain subtyping.

The shipper that provided the oysters harvested elsewhere in Long Island also had
received oysters from Oyster Bay at approximately the same time. Although comingling of
shellfish is against state regulations, it is known to occur.

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